Deposition of soluble materials using ink jet print head and alignment marks

ABSTRACT

The invention provides a method and apparatus for depositing a soluble material, such as an organic polymer, onto a substrate using an inkjet print head. The substrate is provided with an array of alignment marks and the material in solution is deposited when substantially aligned with one of the alignment marks to provide an alignment dot of the material in solution. The alignment dot is viewed before the deposited material in solution has dried. Cross-shaped alignment marks are used to facilitate viewing of the positions of the alignment dot.

BACKGROUND

The present invention relates to the deposition of soluble materials andin particular to the deposition of soluble materials using inkjettechnology.

In recent years there has been an increase in the number of productswhich require, as part of their fabrication process, the deposition oforganic or inorganic soluble or dispersible materials such as polymers,dyes, colloid materials and the like on solid surfaces. One example ofthese products is an organic polymer electroluminescent display device.An organic polymer electroluminescent display device requires thedeposition of soluble polymers into predefined patterns on a solidsubstrate in order to provide the light emitting pixels of the displaydevice. The substrate may, for example, be formed of glass, plastics orof silicon.

In the manufacture of semiconductor display devices, such as lightemitting diode (LED) displays, it has been conventional to usephoto-lithographic techniques. However, photo-lithographic techniquesare relatively complex, time consuming and costly to implement. Inaddition, photo-lithographic techniques are not readily suitable for usein the fabrication of display devices incorporating soluble organicpolymer materials. Concerns relating to the fabrication of the organicpolymer pixels have, to some extent, hindered the development ofproducts such as electroluminescent display devices incorporating suchmaterials to act as the light emitting pixel elements. Consequently, ithas been proposed to use inkjet technology to deposit the solubleorganic polymers in the fabrication of electroluminescent displaydevices.

SUMMARY

Inkjet technology is, by definition, ideally suited to the deposition ofthe above soluble or dispersible materials. It is a fast and inexpensivetechnique to use. In contrast to alternative techniques such as spincoating or vapour deposition, it instantly provides patterning withoutthe need for an etch step in combination with a lithographic technique.However, the deposition of the soluble organic materials onto the solidsurface using inkjet technology differs from the conventional use of thetechnology, to deposit ink on paper, and a number of difficulties areencountered. In particular, there is a primary requirement in a displaydevice for uniformity of light output and uniformity of electricalcharacteristics. There are also spatial limitations imposed in devicefabrication. As such, there is the non-trivial problem to provide veryaccurate deposition of the soluble polymers onto the substrate from theinkjet print head. This is particularly so for colour displays asrespective polymers providing red, green and blue light emissions arerequired to be deposited at each pixel of the display.

To assist the deposition of the soluble materials it has been proposedto provide the substrate with a layer which includes a pattern of wallstructures defined in a de-wetting material so as to provide an array ofwells or elongate trenches, bounded by the wall structures, forreceiving the material to be deposited. Such a pre-patterned substratewill be referred to hereinafter as a bank structure. When organicpolymers in solution are deposited into the wells, the difference in thewettability of the organic polymer solutions and the bank structurematerial causes the solution to self align into the wells provided onthe substrate surface. However, it is still necessary to deposit thedroplets of organic polymer material in substantial alignment with thewells in the bank structure. Even when such a bank structure is used,the deposited organic polymer solution adheres to some extent to thewalls of the material defining the wells. This causes the central areaof each deposited droplet to have, at best, a thin coating of depositedmaterial, perhaps as low as 10% of the material in comparison to thematerial deposited at the walls of the bank structure. The depositedpolymer material at the centre of the wells acts as the active lightemissive material in the display device and if the polymer material isnot deposited in accurate alignment with the wells, the amount andtherefore the thickness of the active light emissive material can befurther reduced. This thinning of the active light emissive material isof serious concern because the current passing through the material inuse of the display is increased which reduces the life expectancy andthe efficiency of the light emissive devices of the display. Thisthinning of the deposited polymer material will also vary from pixel topixel if deposition alignment is not accurately controlled. This givesrise to a variation in the light emission performance of the organicpolymer material from pixel to pixel because the LED's constituted bythe organic material are current driven devices and, as stated above,the current passing through the deposited polymer material will increasewith any decrease in the thickness of the deposited material. Thisperformance variation from pixel to pixel gives rise to non-uniformityin the displayed image, which degrades the quality of the displayedimage. This degradation of image quality is in addition to the reductionin operating efficiency and working life expectancy of the LED's of thedisplay. It can be seen therefore that accurate deposition of thepolymer materials is essential to provide good image quality and adisplay device of acceptable efficiency and durability.

The requirement to achieve accurate alignment of the print head nozzleswith the wells in the bank structure can, in practice, be subdividedinto two parts; namely preparation alignment and printing processalignment, this latter alignment being achieved through actualdeposition of material.

The preparation alignment may itself be broken down into two stages. Thefirst stage may be termed ‘alignment in θ’ and this is carried out toensure that the substrate carrying the bank structure and thetranslation system carrying the inkjet head are aligned both in thetransverse (X) and longitudinal (Y) directions of the substrate. Thisalignment in θ is carried out optically by aligning the print head witha first well in the bank structure located at or in the vicinity of acorner of the structure.

The wells in the bank structure may be considered as a matrix array ofrows and columns and the print head is positioned firstly at theopposite end of the row in which the first well is located and thealignment of the print head with a second well in the row is checked.This can be referred to as alignment in the X direction. The print headis then positioned over the opposite end of this column containing thefirst well and the alignment with a further well at this opposite end ofthe column is checked. This is referred to as alignment in the Ydirection. If misalignment is observed the substrate is rotated relativeto the head translation system in the plane of the substrate and theabove observation process is repeated until optical alignment is seen inboth the X and Y directions of the substrate.

There are two main types of inkjet head. One type uses a thermal printhead and these are commonly known as bubble jet heads. The second typeuses a piezoelectric print head where a piezoelectric device is locatedbehind a diaphragm in communication with a reservoir. In this secondtype of inkjet head the piezoelectric device is energised and thediaphragm deflects to pressurise the reservoir, forcing the liquidcontained in the reservoir, in this case the polymer material insolution to provide the light emissive pixels for a display, out througha nozzle as a fine droplet of the polymer material. With either type ofprint head, the nozzle has a very small outlet orifice, typically of adiameter of about 30 microns. The organic polymers are usually dissolvedin a relatively volatile organic solvent so that they can be depositedin solution.

During deposition, the inkjet print head is maintained as close aspossible to the substrate carrying the bank structure. Normally, theinkjet print head is arranged at a separation of about 0.5 mm to 1.0 mmabove the substrate. This separation range may also be used to initiallycheck optically the alignment of the print head in θ as described above.The wells in the bank structure are however very small in size so a highmagnification microscope is required for this optical alignment check.As high magnification is used, there is very little depth of field inthe viewed image and hence, it is usually not possible to have a well inthe bank structure and the nozzle of the inkjet head in focus at thesame time, which makes it difficult to ensure that the required opticalalignment is actually being achieved.

It is also necessary to ensure that the viewing axis is exactlyperpendicular to the substrate, otherwise an offset occurs between awell and a nozzle of the ink jet head. This also is very difficult toachieve in practice.

The second stage of preparation alignment may be termed as ‘alignment toobtain the origin’, the origin being the position where deposition ofthe organic polymer material is to commence in the fabrication of thedisplay device. However, it can be appreciated from the above concernsthat optical alignment of an inkjet head with wells of the bankstructure cannot be readily achieved with the required accuracy.

The alignment of origin is therefore usually carried out with actualdeposition of one or more droplets of the organic polymer material. Thematerial is deposited into a number of wells in the bank structure andthe alignment is checked by subsequently viewing the deposited droplets.However, a number of concerns also arise with actual deposition ofmaterial to achieve alignment of origin.

A droplet of material, when dry, has the same wetting property assubsequent droplets being deposited. Hence, if a wet or fresh dropletcontacts a previously deposited dry droplet it may be pulled towards thedeposition site of the previous droplet, making it. extremely difficultto check the actual deposition site of the later deposited droplet.Furthermore, the droplets of deposited material, when dry, are verydifficult to see even with a microscope, because they are very thin andrelatively transparent. Also, the wells in the bank structure aresubstantially circular in shape, as are the deposited droplets. Hence,if a droplet is deposited into exact alignment with a well in the bankstructure, it is, in essence, a substantially circular droplet of arelatively transparent material located in a substantially circularshaped well in the bank structure. There is therefore a significant needfor an alternative arrangement to check alignment of origin, such as acompact array of alignment marks separate from the wells in the bankstructure. If the coordinates between the marks of such an alignmentarray are known, then this information can be used to apply correctionto the deposition head to achieve the origin. Furthermore, if thealignment array is arranged such that the spacing between marks is inthe region of between about 2 to about 10 times the size of depositeddroplets, several of such marks can be viewed simultaneously in thefield of view of the microscope being used to obtain the origin,enabling several deposited droplets to be checked without repositioningof the viewing microscope.

Once the preparation alignment has been completed the actual printingprocess may commence. However, as will become apparent form thedescription below, printing process alignment needs to be carried out atregular intervals during actual printing or deposition of the droplets.In inkjet printing the droplets have a flight speed typically in therange of 2 to 10 m/sec. The relative speed between the substrate andprint head is typically in the range of 10 to 100 mm/sec. Assuming adroplet speed of about 5 m/sec and a separation of 1 mm between theinkjet head and substrate, the time taken for an ejected droplet toreach the substrate is about 0.2 milliseconds. If the print head has atransverse speed of 100 mm/sec relative to the deposition substrate, anoffset of 20 μm will be created between the ejection point and theactual deposition point on the substrate. This offset, if considered inisolation, is regular and equal for all nozzles of the inkjet printhead. For conventional printing, in which case the substrate is paper,which is the normal use of this technology, this offset is notproblematical because it is the same over the entire printed image andsuch a small offset in the position of the printed image on the paper isnot discernible during normal viewing of the printed data image.

However, with the printing of organic polymer devices, the organicpolymers are dissolved in a relatively volatile solvent and someevaporation of the solvent will occur as the solution ejects from thenozzle outlet orifice. Hence, it is common for deposits of the polymermaterial to form around the orifices of the inkjet nozzles. Thesedeposits tend to form in an uneven fashion and therefore give rise to anirregular profile for the periphery of the nozzle orifice, causing adeflection of the material as it ejects from the print head nozzle.Because of the deflection to the ejected solution, the ejected dropletsinvariably do not have a perpendicular flight angle relative to thesubstrate. This gives rise to further but irregular offsets between thedesired and actual positions of a deposited droplet on the substrate.Furthermore, the deposits around the nozzle orifice usually vary duringthe deposition process and likewise, therefore, the offset between thedesired and actual deposition sites can also vary in an irregular mannerover the period during which the droplets are deposited. There is,therefore, a significant need to repeatedly monitor the deposition ofdroplets to ensure that the required accuracy of deposition is beingmaintained during device fabrication. If deposition accuracy isdetermined as not being maintained the nozzles of the inkjet head mustbe cleaned of the deposits. This irregular offset between the positionof the inkjet head and the deposition site gives rise to a furtherconcern regarding checking alignment of the inkjet head nozzles with thewells in the bank structure.

The inkjet head usually comprises an array of nozzles so that as thehead is translated over the deposition area, several droplets of theorganic polymer are deposited simultaneously. However, because the buildup of deposits is totally random in nature, the irregular offset for afirst nozzle of the head may be in one direction (compared to the flightpath for the nozzle without any build up of deposit), for examplecausing the ejected droplet to travel further in the direction of travelof the inkjet head, whilst the deposit at a second nozzle of the headmay, for example, cause an offset in a direction opposite to the firstdirection, i.e. in a direction opposite to the direction of travel ofthe head. As stated above, there is a regular offset caused by theflight time of a droplet and the speed of movement of the inkjet head.If, for example, the substrate is moving relative to the head, a dropletwould actually be deposited to one side of the target well in the bankstructure because the well would have moved past the flight path contactpoint by the time the droplet has traversed the separation gap betweenthe head and the substrate. This is the regular offset referred to aboveand this can be compensated during initial optical alignment. However,if the regular offset is cancelled by the irregular offset caused by thedeposit, and if this particular well in the bank structure is viewedafter deposition of a droplet, it would give the impression that thereare no alignment concerns because the deposited droplet may appear to beperfectly aligned in its target well in the bank structure, but this isdue to the irregular offset which may vary during the depositionprocess.

However, the irregular offset for the second nozzle is in the oppositedirection to that of the first nozzle. Hence, in this second case, theregular and irregular offsets would be cumulative and could provide anunacceptable degree of misalignment between the droplets being ejectedfrom the second nozzle and their target wells in the bank structure, butthis unacceptable alignment would not be noticed because the alignmentcheck on the first droplet has indicated that the inkjet head iscorrectly aligned with the bank structure. These irregular offsets canbe particularly problematical in the production of relatively large sizeelectroluminescent display devices, because deposition is required tooccur over a longer period of time and there is therefore an increasedlikelihood of variable offsets.

If the substrate is of a relatively large size further irregular offsetsmay be introduced due to thermal expansion or contraction of thesubstrate, such as those arising from changes in the ambient conditionsin the deposition zone.

Additional variable offsets may also be caused by bending of thetranslation system for the inkjet head. As can be seen from FIG. 1, theinkjet print head is supported from a transverse beam which is usuallydisposed horizontally. The beam, being a physical structure, bends veryslightly under gravitational forces. The centre part of the beam willsubstantially maintain its horizontal disposition so a droplet depositedwith the print head positioned at a central location A will maintain aperpendicular flight path A¹, as shown in FIG. 2, to the substrate.However, as the print head is translated away from this central part ofthe beam, such as to position B shown in FIG. 2, it will no longer besupported by a truly horizontal beam so the flight path B¹ at thissecond position B will no longer be perpendicular to the substrate.Hence, if the print head is moved by X cm along the beam, this can giverise to a variation in deposition point of X+α at the substrate, where αis the additional variable offset caused by the slight bending of thebeam. This variable offset can be seen to be present even on relativelysmall substrates and as the substrate becomes larger, the offset becomeseven more noticeable because the translation system becomes longer,giving rise to an increase in the deviation from a perpendicular flightpath to the substrate.

All of the above offsets may give rise to a variation from the optimumthickness for the organic material in the well in the bank structure,which as stated above, can create non-uniformity in the displayed imageand hence, a display of unacceptable image quality.

As mentioned above, a pattern of wells of bank material may be used tophysically assist the alignment of the deposited polymer materials.However, polymer material can only be deposited in each well once andthe wells ultimately form the active pixels of the display device.Hence, if misalignment does occur to an unacceptable level it is notpossible to reposition the ejection nozzle above any particular well ofthe bank structure noticed as being defective and for a further dropletof the polymer material to be deposited in the defective well.Therefore, if any droplet of deposited polymer material is not inalignment with its respective well, a defective well of polymer materialwill already have been created on the substrate in the region whichultimately is to provide part of the active area of the final displaydevice, degrading displayed image quality.

There are also significant difficulties associated with the viewing ofthe polymer material, when dry, as will become clear from thedescription below. Therefore, there is a significant need to be able tomonitor the deposition of the organic polymer material in thefabrication of electroluminescent display devices at, or very shortlyafter deposition actually occurs. This can be referred to as in-situviewing.

However, as mentioned above, in-situ viewing of deposited droplets inthe wells of the bank structure can present further difficulties becausethe wells and the deposited droplets are both circular in shape.

However, the organic polymer material can be deposited in each well ofthe bank structure once only, so if in-situ viewing is carried out anddeposited droplets are seen to be out of alignment, the inkjet headcannot be tracked back over an improperly aligned well for a furtherdroplet of material to be deposited in order to correct themisalignment. It has been realised therefore that a separate array ofalignment marks can be used advantageously to check droplet alignmentboth for alignment in origin and during the printing process. If suchalignment marks are provided, alignment of origin can be achieved moreeasily and with improved accuracy and, furthermore, the depositionaccuracy can be checked periodically, and any misalignment seen to occuron an alignment mark or sensed as being likely to occur, such as atendency for an alignment drift between deposition of material on onealignment mark and a subsequent alignment mark, can be used to providecompensatory control to the inkjet head position and provide correctionfor misalignment before it reaches a condition where it would give riseto defective pixels in the display device.

These marks of the alignment array for use during the printing processcan be provided alongside the edges of the active area to be printedand, optionally, they may also or alternatively be provided within theactive area to be printed. Furthermore, the alignment marks can beprovided with a specific shape to ease in-situ viewing.

According to a first aspect of the invention, there is provided a methodof selectively depositing a material dissolved or dispersed in asolution on a first area of a first surface of a substrate using aninkjet print head, the method further comprising providing an array ofalignment marks on the substrate, depositing the material onto the firstsurface of the substrate from the ink jet print head when substantiallyaligned with one of the alignment marks thereby to provide an alignmentdot of the material, and detecting the alignment dot relative to thealignment mark.

Advantageously, the alignment dot of material is viewed as it depositson the first surface of the substrate.

Preferably, the alignment dot of material is detected prior to thematerial changing from a wet condition to a dry condition.

In preferred aspects of the invention the alignment marks are providedas a matrix array or a linear array of alignment marks. Preferably, thealignment marks are provided as cross shape alignment marks.

In a preferred form of the invention, the soluble material is selectedto comprise a conjugated polymer. Advantageously, the further surface ofthe substrate is irradiated with light of a wavelength to which thesubstrate is substantially transparent when viewing an alignment dot ofthe soluble material in a wet condition.

Preferably, the further surface of the substrate is illuminated suchthat the alignment dots of soluble material are viewed as bright fieldimages.

When the soluble material comprises a conjugated polymer, the light isselected to have a wavelength which is greater than the wavelength ofthe absorption edge of the conjugated polymer.

In a preferred form of the invention, the alignment mark(s) is/areprovided to have optical contrast but no wettability contrast relativeto the substrate.

In a most preferred aspect of the invention, there is provided a methodfor making an electronic, opto-electronic, optical or sensor deviceusing the method according to the first aspect of the present invention.

According to a second aspect of the invention, there is provided asubstrate for use in the method according to the first aspect of thepresent invention.

According to a third aspect of the present invention there is providedan electronic, opto-electronic, optical or sensor device comprising asubstrate according to the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of further exampleonly and with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of an inkjet deposition machine inwhich. deposition of a soluble material onto a substrate may be directlyobserved;

FIG. 2 shows the variable offset which can be produced by bending of theinkjet head translation system of the machine shown in FIG. 1;

FIG. 3 shows a plan view of part of a substrate having a bank pattern ofwells and illustrating examples of dry and recently deposited dropletsof polymer material;

FIG. 4 illustrates schematically an inkjet print head showing thedeviation in the flight path of an ejected droplet;

FIG. 5 shows an embodiment of a substrate including alignment marksaccording to the present invention;

FIG. 6 shows an alternative embodiment of a substrate includingalignment marks;

FIGS. 7 to 9 show embodiments of cross shape alignment marks;

FIG. 10 shows a droplet of polymer material in a wet condition on asubstrate;

FIG. 11 shows schematically a bright field imaging system;

FIG. 12 shows the droplet of FIG. 10 when viewed as a bright fieldimage;

FIG. 13 shows a droplet of polymer material in a dry condition on asubstrate;

FIG. 14 shows the droplet of FIG. 13 when viewed as a bright fieldimage;

FIG. 15 shows schematically a dark field imaging system;

FIG. 16 shows the droplet of FIG. 10 when viewed as a dark field image;

FIG. 17 shows the droplet of FIG. 13 when viewed as a dark field image;

FIG. 18 shows absorption and luminescence characteristics for aconjugated polymer material;

FIG. 19 shows part of the polymer chain for a conjugated polymermaterial;

FIG. 20 shows schematically the excitation of electrons of a conjugatedpolymer under incident radiation;

FIG. 21 shows oxidation of the polymer chain illustrated in FIG. 9;

FIG. 22 shows a deposited droplet on an alignment mark as illustrated inFIG. 9 when viewed as a bright field image;

FIG. 23 shows a block diagram of an electrooptic device;

FIG. 24 is a schematic view of a mobile personal computer incorporatinga display device fabricated in accordance with the present invention;

FIG. 25 is a schematic view of a mobile telephone incorporating adisplay device fabricated in accordance with the present invention; and

FIG. 26 is a schematic view of a digital camera incorporating a displaydevice fabricated in accordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, an inkjet deposition machine 1 comprises a base 2supporting a pair of upright columns 4. The columns 4 support atransverse beam 6 upon which is mounted a carrier 8 supporting an inkjetprint head 10. The base 2 also supports a platen 12 upon which may bemounted a substrate 14. The platen 12 is mounted from the base 2 via acomputer controlled motorised support 16 for effecting movement of theplaten 12 both in a transverse and a longitudinal direction relative tothe inkjet print head, as shown by the axes X and Y in FIG. 1.

In accordance with the present invention, the base 2 also supports acharge coupled device (CCD) microscope 18 which is arranged below andslightly offset from the platen 12 for viewing the lower or undersurface of the substrate 14 via a mirror 20. Equally, the CCD microscopecould be arranged vertically under and arranged to move in unison withthe platen 12, obviating the need for the mirror 20. Optionally, theinkjet deposition machine 1 also includes a second CCD microscope 22 anda stroboscope 24 mounted from the base 2. The carrier 8 is movable alongthe transverse beam 6 such that the inkjet head 10 can be positioned inthe space between the CCD microscope 22 and the stroboscope 24 so thatthe ejection of droplets from the inkjet head 10 can be observeddirectly. This is to enable the driving condition of the inkjet head 10to be tuned for various solutions and polymers which may be required tobe ejected on to the substrate 14. As the movement of the platen 12, andhence the substrate 14 relative to the inkjet head 10, is under computercontrol, arbitrary patterns may be printed onto the substrate byejecting appropriate materials from the inkjet head 10.

FIG. 3 shows an enlarged view of part of the substrate 14. It can beseen from FIG. 3 that the substrate 14 carries a pre-pattern in the formof an array of wells 26 of bank material which receive the organicpolymer material ejected from the ink jet head 10. The use of bankpatterns is well known in this art and will not, therefore, be describedfurther in the context of the present invention. As will be appreciated,to achieve the required resolution in a display device, thephotoluminescent organic polymers, which form the light emitting diodesat each pixel, must be very accurately deposited on the substrate 14.This is particularly so for a colour display, because individual spotsof polymer material emitting red, green or blue light must be providedat each pixel of the display to provide a colour image. Typically, insuch a display device the organic polymer is a conjugated polymer andmay comprise, for example, F8/F8BT/TFB where F8 is[poly19,9-dioctylfluorene)-], F8BT is[poly9,9-dioctylfluorine-co-2,1,3-benzolthiadizole)], and TFB is[poly19,9-dioctylfluorine-co-N-(4-butylphenyl)diphenylamine)].

The bank material defining the wells 26 has a de-wetting surface,whereas the wells 26 themselves have wetting surfaces. Relatively goodconfinement and alignment of the polymer materials can thus be achieved,as can be seen from FIG. 4. However, referring to FIG. 3, the inkjetprint head 10 typically comprises a reservoir 28 for accommodating thepolymer material to be ejected through a nozzle 30, which, typically,has an ejection orifice of approximately 30 microns diameter. As statedabove, for the fabrication of an electroluminescent display device thematerial to be ejected is an organic polymer dissolved in a suitablesolvent, such as Toluene or Xylene. Such solvents are relativelyvolatile and it will be appreciated that the volume of the ejecteddroplets is very small, typically in the order of a few picolitres. Asthe polymer mix is ejected, a bubble of the polymer in solution formsinitially at the nozzle 30 due to the surface tension of the solution.As the pressure within the inkjet head increases, the surface tension isovercome and a droplet of the polymer in solution is separated from thenozzle and ejected from the inkjet head. Partial evaporation of thesolvent occurs whilst the bubble of solution is in contact with thenozzle causing some of the ejected polymer material to form a deposit 32at the exit orifice of the nozzle 30. The deposit 32 forms in anirregular fashion and can cause an ejected droplet 34 to follow anon-vertical path, shown by the arrow in FIG. 4, onto the substrate,creating an offset between the actual and the required deposition site,i.e. the well 26. Some clogging of the nozzle 30 is a common occurrencein inkjet heads and to minimise the affect of the non-vertical flightpath of the ejected droplets 34, the inkjet print head 10 is maintainedas close as possible to the substrate 14 during the deposition cycle.However, a finite separation between the print head and substrate mustnecessarily be maintained, which gives rise to a deviation or offsetbetween the actual and target deposition sites. Furthermore, in thefabrication of large area displays, flexible plastics sheets or flexibleplastics in spoolable roll form can be particularly advantageous. Suchflexible plastics substrates may be positioned over a rigid planarsurface or may be tensioned in order to present a flat substrate fordeposition under the print head. In either case distortion of thesubstrate has been found to occur and this distortion can vary as thesubstrate is being moved under the print head. Additionally, suchsubstrates change in physical size with variations in ambientconditions, such as temperature and humidity. All of these factors canalso give rise to a deviation or offset between the actual and targetdeposition sites of the droplets.

It can be seen, therefore, that there is a significant need to monitorthe deposition of the droplets of organic polymer material onto thesubstrate. The accuracy to which droplets have been deposited may bechecked by viewing the droplets after deposition onto the bank structureusing a suitable microscope. It is also possible to view depositeddroplets periodically from the deposition side of the substrate.However, the inkjet head typically consists of an array of ejectionnozzles. Because of the physical size of the ink jet head and theobjective lens of the viewing microscope, there is necessarily someseparation distance between the current droplets being deposited and thedroplets being viewed. There is also a considerable time delay betweenactual droplet deposition and viewing. The droplets are of very smallvolume and contain a high proportion of volatile solvent. Therefore theydry relatively quickly once deposited. Hence, the deposited dropletshave invariably attained a dry or relatively dry condition by the timethey can be viewed and are very difficult to distinguish in the bankstructure, especially when the deposited materials are transparent.

There is an added concern in viewing droplets deposited into the wellsof the bank structure. The droplets can move as they dry. A dropletconsists typically of 1% to 5% by volume of organic polymer material,the remaining 95% to 99% being solvent. It can be appreciated thereforethat once a droplet has dried the actual material remaining on thesubstrate is of far smaller volume than the volume of the dropletactually deposited onto the substrate. The material remaining alsooccupies a much smaller area than the droplet as deposited. If thesurface of the substrate is uniform then the material which remains as adry droplet of organic polymer is usually positioned at the centre ofthe area occupied by a droplet as deposited. However, if the surface ofthe substrate includes non-uniformities, which is frequently the case,and particularly for plastics substrates, the polymer material in thedeposited droplet can be attracted by a non-uniformity during the dryingprocess. The dried material remaining on the substrate can therefore bedisposed to one side or an extremity of the area occupied on thesubstrate by a droplet as deposited, or it may remain substantially atthe centre, depending upon the position of the non-uniformity.Furthermore, the material of the bank structure is chosen so as toprovide high wettability contrast with the material being deposited.This wettability contrast is provided to improve the accuracy with whichthe deposited droplets are aligned with the wells in the bank structureand thus attain their required positions on the substrate. However, thewettability contrast, by way of its required function, influences theposition of droplets deposited onto the bank structure. Hence, viewingof a dried droplet in the bank structure is not a true. indication ofdeposition alignment because, for a particular deposited droplet, theorganic polymer material may have “moved” into exact alignment with atarget deposition site during the drying process because of the abovedescribed influences at the position where the droplet was actuallydeposited.

It can also occur that this movement of a droplet can give rise to nooverlap between the target well in the bank structure and a partiallydry deposited droplet, in which case the contrast in the wettabilitybetween the droplet and the material of the bank structure is negated,making it more difficult for the droplet to align in the well of thebank structure.

It has been proposed to view deposited droplets in the bank structure bytemporarily moving the inkjet head from the area being deposited andthen positioning a suitable microscope over the last deposited droplets.However, this proposal has proved problematical because the droplets drybefore the microscope can be moved to the viewing position and, as thedisplay size increases, it becomes particularly difficult to determinethe position of the last deposited droplets on the substrate. Aprincipal reason for this is that the dry polymer material cannot bedistinguished easily from the substrate or bank structure materials.

Furthermore, to repeatedly move the inkjet head away from and back tothe deposition location is not efficient and there is no real timemonitoring of deposition so feedback on the viewing cannot be maximised.

However, as mentioned above, the polymer material can be deposited ineach well of bank material once only so even if deposited droplets areseen to be out of alignment, the inkjet head cannot be tracked back overthe badly aligned wells of material for further droplets to be depositedin order to compensate the misalignment.

Furthermore, alignment of origin is usually carried out with actualdeposition of one or more droplets into wells of the bank structure.Because the wells of the bank structure are used to form the actualpixels of the display, each well used to check alignment of origindegrades the image quality because the wells used for alignment checkcannot be used subsequently to provide light emitting pixel elements.For this reason, the number of wells used for alignment of originconfirmation is usually kept to a minimum and this small number can befound to be insufficient to adequately check alignment of origin.Additionally, the wells in the bank structure and the deposited dropletsare circular in shape so even if in-situ viewing is needed for alignmentof origin confirmation, the concern of trying to view circular dropletsin circular wells continues to be manifest. Furthermore, the wettabilitycontrast of the bank structure material may have a significant influenceon a deposited droplet and thus, use of the bank structure can give afalse indication of alignment of origin.

Hence, it has also been realised in the present invention that there isa significant need for an array of alignment marks on the substrate, inaddition to the bank pattern of wells in which, for example, the activepixels of a display are created, and these alignment marks can be. usedselectively to monitor in-situ deposition of the polymer material, bothduring alignment of origin and printing of the pixel elements, and tosubsequently control the positioning of the inkjet print head relativeto the substrate during the deposition of the polymer materials into thepattern of wells of bank material on the substrate.

In a preferred form of the present invention, as shown in FIG. 5, thesubstrate 14 is provided with two arrays of alignment marks, such as acompact matrix array 46; located at or near to the origin on thesubstrate, and a linear array of alignment marks 48 located along theedge of the substrate and these can be viewed from the underside of thesubstrate, during actual deposition of polymer material. The lineararray 48 of FIG. 5 is shown along both edges of the substrate but,equally, the array may be provided only along one edge of the substrate.Likewise, although a single. matrix array 46 is shown, similar matrixarrays may also be provided at other locations on the substrate, such asat or near the corners of the substrate or periodically along the edgeof the substrate. Therefore, for large substrates, such as webs ofplastics material, several of such alignment arrays may be provided atspaced locations on the substrate.

The matrix array 46 has been found to be particularly beneficial forachieving alignment of origin as the array can be provided in a cornerregion of the substrate outside of that or those areas of the substratewhich will be used to provide the display areas of display devices.Furthermore, if the marks of the array are spaced at between about 2 to10 times the pitch of the wells in the bank structure, the alignment oforigin can be easily checked using in-situ viewing. With regard to thelinear arrays along the edges of the substrate, these have been found tobe particularly beneficial for checking alignment during actual printingof the polymer dots which ultimately will be used to form the activepixel elements of the display device as the alignment can beperiodically checked throughout the printing process by moving theinkjet head a short distance so as to overlie one of the linear arrayalignment marks. One or more linear arrays, such as the array 49 shownin FIG. 6, may also be provided in the central region of the substrateused to provide the display area of the display device.

It has been found with the present invention that a cross shapealignment mark is particularly suitable for checking alignment, as shownin an enlarged size in FIG. 7. By using a cross shape alignment mark theregistration, and hence any unwanted offset, of a deposited droplet canbe more easily checked with reference to the cruciform area at thetarget centre of the cross shape alignment mark.

To further assist this alignment process, leg portions 50 of the crossshape marks can be made of tapering shape 52, each reducing in widthbetween distal ends 54 and proximal ends 56, as shown in FIG. 8. A crossshape mark having three leg portions, as shown in FIG. 9, has been foundto be particularly beneficial as the central target portion is stillapparent but there is less pull on a deposited droplet arising from thethree leg portions 50 in comparison to an alignment mark having four legportions.

It can be seen from FIGS. 7 to 9 that the leg portions 50 aresymmetrically spaced in a circumferential direction about the centre ofthe mark. Hence, for the three leg mark shown in FIG. 9, the legportions are mutually spaced at an angle α of 120° in thecircumferential direction.

The cross shape marks shown in FIGS. 7 to 9 provide a distinct shape incontrast to the circular shape of a deposited droplet. Furthermore, theleg portions, particularly those of tapering shape as shown in FIGS. 8and 9, draw visibly towards the centre of the mark whilst also providingvisual discernible divisions in a deposited droplet. This makes it fareasier to spot misalignment of a deposited droplet with any alignmentmark, particularly in comparison to checking alignment of a depositeddroplet using the circular wells of the bank structure.

Furthermore, the alignment marks can, unlike the bank structure, beprovided of a material which provides high optical contrast with adeposited droplet but low or no wettability contrast with a depositeddroplet. Additionally, because the alignment marks can be provided to aspecific design, such as the cross-shaped marks described, an imagerecognition technique can advantageously be used to detect the alignmentmarks and deposited droplets serving as alignment dots. Any suitableimage recognition technique may be used, such as scanning areas of thesubstrate where the alignment marks are known to be provided andcomparing data derived from the scanning process with data stored in amemory, such as a programmable ROM provided in the inkjet machine. Suchtechniques are well known and will not, therefore, be described furtherin the context of the present invention. However, it will be apparentthat, unlike the bank structure, because the alignment marks can beprovided with discernible optical contrast, such an image recognitiontechnique can be used to particular advantage with the present inventionand can significantly assist automated checking of alignment accuracyduring device fabrication.

The deposited droplets are far easier to detect when in the wetcondition, that is between deposition and attaining their dry condition,but are extremely difficult to detect after the dry condition has beenattained, and that this characteristic of the deposited droplets of thepolymer material can also be exploited to significant advantage with thepresent invention in order to check the accuracy of deposition of thepolymer material.

The polymer material changes quickly to the dry condition afterdeposition and to exploit this characteristic of the polymer materialsin the wet condition, it is advantageous to view deposited droplets ofmaterial in-situ; that is, at the time they are deposited, in order tobest assess alignment.

The problems associated with viewing deposited polymer material can bemore readily appreciated with reference to FIG. 3. If the polymermaterial has reached its dry condition shown as droplets 38 in FIG. 3 itis difficult to distinguish on the substrate.

However, as can also be seen from FIG. 3, the more recently depositeddroplets i.e. those droplets which have not yet attained a dry conditionfrom the wet condition in which they were deposited, are relatively easyto distinguish. It can be seen also from this figure that, of the tworows 40, 42 of more recently deposited droplets, the last depositeddroplets 44 are the most visible, the visibility decreasing with anincrease of the time since deposition.

The manner in which the deposited droplets are viewed has also beenfound to facilitate checking of alignment accuracy. It is known thatobjects can be viewed as ‘bright field’ or ‘dark field’ images throughthe use of appropriate imaging systems.

FIG. 10 shows a droplet D_(W) of polymer material on a substrate in awet condition. If the wet droplet D_(W) is viewed by a bright fieldimage optical arrangement as shown in FIG. 11 from the underside of thesubstrate, light rays from the imaging light source enter the droplet.Those light rays which are not coincident with the centre axis of thedroplet undergo internal reflection. However, in the region of thecentre axis of the droplet, the upper surface of the droplet issubstantially parallel to the substrate. Hence, those light rays passingin the vicinity of the centre axis of the droplet are able to exit thedroplet through the upper surface in this region of the centre axis.When the droplet is viewed, therefore, it appears as a very bright spotagainst a dark circular ground area, surrounded by the bright fieldbackground, as shown in FIG. 12. The bright spot at the centre of theimage is substantially co-incident with the centre axis of the droplet.This bright field image can therefore be used to advantageous effect todetermine the accuracy to which the droplet has been deposited.

FIG. 13 shows the droplet once it has attained a dry condition,indicated as D_(D) It can be seen that the hemispherical wet dropletD_(W) has assumed the shape of a relatively flat thin disc. If a glasssubstrate, or a plastics substrate having a refractive index similar toglass, is used, the dry droplet has a refractive index which issubstantially the same as the substrate material. In this case slightscattering of the light rays occurs which only gives rise to a slightcontrast at the edges of the droplet, which is relatively difficult todistinguish. However, if the respective refractive indices of theunderstructure and the deposited material are different, and if thebright field imaging system shown in FIG. 12 is used to view the drieddroplet D_(D), the light rays pass into the droplet but undergoreflection at the far side of the droplet. The reflected light raysinterfere with each other and create interference rings of variouscolours, the colours being dependent on the thickness of the droplet.This image is shown schematically in FIG. 14. The image shows ascoloured interference rings which tend to merge with each other in theviewed image. It is relatively difficult, therefore, to discern a sharpoutline for the viewed image. It is readily apparent from a comparisonbetween the wet droplet bright field image shown in FIG. 12 and the drydroplet bright field image shown in FIG. 14, that it is significantlyeasier to check alignment of the deposited droplet using the image ofFIG. 12 than to use the image of FIG. 14.

FIG. 15 shows a dark field imaging system, and if the wet droplet D_(W)shown in FIG. 10 is viewed with this system, light from the light sourceenters the droplet and undergoes reflection within the wet droplet ofmaterial. Some scattering of the light occurs at the edges of thedroplet and hence, the wet droplet appears as a bright but well definedannular ring with a dark centre against a dark background. As the brightring is well defined, the image shown in FIG. 16 is far more beneficialto use to check alignment of the deposited droplet than the bright fieldimage of the dry droplet shown in FIG. 14.

If the dry droplet D_(D) shown in FIG. 13 is viewed with the dark fieldimaging system shown in FIG. 15, most of the light impinging on thedroplet is scattered and passes outside the field of view of the imaginglens. The dried droplet D_(D) appears therefore as a very feint circularimage against a dark background and this image is very difficult to seeand cannot be used to check droplet alignment.

From the above bright and dark field images for the dry and wetdroplets, it can be appreciated that significant and unexpected benefitscan be provided if the deposited droplets are viewed in-situ whilst theyare still in a wet condition. In-situ viewing can be carried out usingthe apparatus shown in FIG. 1. However, the organic polymer materialsare deposited on the upper surface of the substrate, when viewed in FIG.1 and, hence, for in-situ viewing it is necessary to view deposition ofthe polymer materials through the substrate. Viewing of the droplets canbe made easier if the substrate is illuminated with light. As thematerials are viewed through the substrate a first requirement thereforeis that the substrate is transparent at the wavelength of the light usedfor viewing. When the substrate is of glass or transparent plastic,visible light or longer wavelength radiation can be used. When thesubstrate is made of silicon, infra-red light, whose wavelength islonger than 1.1 microns, is required.

There is also a second consideration for in-situ viewing of conjugatedpolymers printed by an inkjet technique. The characteristics forabsorption and emission (luminescence) of light of a conjugated polymerare shown in FIG. 18. It can be seen from FIG. 18 that there is anoverlap region for the absorption and luminescence characteristics. Theconjugated polymer will absorb to varying degrees, light incident uponthe polymer having a wavelength less than λ₁. This is indicated as theabsorption region in FIG. 18. The conjugated polymer is only transparentto incident light having a wavelength greater than λ₁ and this isindicated as the transparent region in FIG. 18.

A conjugated polymer chain is shown in FIG. 19 and delocalised π bondingorbit electrons exist along the chain. These electrons have a relativelynarrow band gap compared to sigma bonding electrons which also exist inthe polymer chain. If the conjugated polymer absorbs Ultra Violet (UV)or visible light, the π bonding electrons are excited from the π bondingorbit (grand state) to a π* anti-bonding orbit (excited state), as shownin FIG. 20. The excited state is less stable than the grand state withrespect to the π bonding between atoms. If oxygen atoms are present andthis excitation occurs, the π bonding is destroyed and some bondingtakes place between the oxygen atoms in the ambient atmosphere and thecarbon atoms of the conjugated polymer, giving rise to the photooxidised polymer chain shown in FIG. 21. This bonding can occur whenthere are oxygen atoms in the ambient atmosphere of the conjugatedpolymer and the light to which the conjugated polymer is exposed has acomponent in the absorption region for the conjugated polymer, i.e. acomponent having a wavelength less than λ₁ shown in FIG. 18.

The bonding between the oxygen and carbon atoms degrades the conjugatedpolymers which gives rise to lower luminance efficiency in LED's andlower charge mobility for organic thin film transistors (TFT's). Oneoption to obviate this polymer degradation is to print the conjugatedpolymers in an atmosphere which does not contain oxygen. This entailslocating the apparatus shown in FIG. 1 in a chamber where the ambientatmosphere within the chamber can be carefully controlled to ensure nooxygen is present. However, this increases process complexity and,furthermore, increases fabrication costs. It is therefore a morerealistic proposition to control the wavelength of the light used forin-situ viewing to be in the transparent region of the conjugatedpolymer, i.e. a wavelength greater than λ₁ shown in FIG. 18.

When a multi-colour display is manufactured, the red light emittingpolymer has the narrowest band gap (longest wavelength for theabsorption edge λ₁). In this case, the light used in the imaging systemfor in-situ viewing of droplet deposition should not involve a spectralcomponent having a wavelength shorter than the wavelength of theabsorption edge for the red light emitting polymer. Furthermore, thesilicon detector of the CCD microscope decreases in sensitivity with anincrease in the wavelength of the light used and becomes transparentwhen the incident light has a wavelength of about 1.1 μm. A wavelengthof about 900 nm has been found to continue to provide acceptablesensitivity for the CCD. Hence, for a multi-colour display, deep red orinfra-red light having a wavelength in the range of about 600 nm toabout 900 nm should be used to avoid photo oxidation and thereforedegradation of the red light emitting polymer.

Hence, if in-situ viewing of the deposited droplet before the drycondition is used, any offset between the deposited droplet and a wellin the bank structure can more easily be seen. Furthermore, as thepotential offset in the deposited material can be monitored throughoutthe duration of the deposition cycle, any increase in offset to beyond atolerable limit may be quickly detected and appropriate positionalcompensation between the platen and the inkjet head may be provided bythe computer controlled motorised support 16.

Additionally, if a bright field imaging system is used for in-situviewing, a bright spot is very discernible at the centre of the brightfield image. Hence, if bright field imaging is used to view depositeddroplets, the location of the bright central spot relative to thecentral portion of the cross shape alignment mark becomes verynoticeable, facilitating the alignment check. Moreover, because thealignment marks, and particularly those of the matrix array 46 used fororigin alignment check, can be spaced advantageously at a pitch at up to10 times the diameter of deposited droplet, the leg portions can bearranged to be relatively thin but having a length slightly greater thanthe anticipated radius of a deposited droplet. When in-situ viewing isused, this gives rise to a bright field image against an alignment markas shown in FIG. 22, making it relatively easy to check alignment. Thebright field image in FIG. 22 is illustrated in the same way as thebright field image in FIG. 12.

Referring again to FIG. 1, in use, the ink jet head 10 is fed with anappropriate supply of the polymer material to be deposited. Thesubstrate 14, preferably including an array of wells 26 in the area ofthe substrate in which the polymer material is to be deposited, isrigidly mounted on the platen 12. The platen 12 is moved in the X and Yaxes by way of the computer controlled motorised support 16 andalignment in θ is achieved optically. The inkjet head is then locatedselectively over one of the matrix arrays 46 and the polymer material isdeposited onto the alignment marks of the matrix array to checkalignment of origin. The ink jet head is then located over the wells ofthe bank structure and the polymer material is ejected by the inkjetprint head 10 to form the pixel elements of the display. Periodicallyduring the formation of the active pixel elements, the platen 12 ismoved under computer control to a position such that an alignment mark46 of one of the linear arrays 46 is substantially aligned under thenozzle 30 of the inkjet head 10. For example, this may occur each timethe polymer material has been deposited in a predetermined number ofrows of the wells 26. The deposition of the ejected droplets onto thealignment marks is viewed from the underside of the substrate 12 by theCCD microscope 18 via the mirror 20. As there is in-situ viewing of thedeposited droplets before the dry condition is attained, and because aspecifically shaped alignment mark is used, any offset between thedeposited droplet and the alignment mark can more easily be seen.Furthermore, as the potential offset in the deposited material ismonitored throughout the duration of the deposition cycle, any increasein offset to beyond or approaching a tolerable limit may be quicklydetected and appropriate positional compensation between the platen andthe inkjet head can be provided by the computer controlled motorisedsupport 16. The fabrication of active pixel elements with unacceptableoffset can therefore be minimised.

As will be appreciated from the above deposition, the polymer materialis deposited onto the upper or first surface of the substrate whereasthe actual deposition is viewed from the lower surface of the substrateopposite to the upper surface. The substrate may comprise glass or atransparent plastics material which means that visible light can be usedto view the deposition. Equally, the substrate may comprise a silicon orother non-transparent substrate in which case the substrate can beirradiated with light having a wavelength to which the substrate istransparent, e.g. infra-red radiation for a silicon substrate to enablethe in-situ deposition to be viewed through the otherwise opaquesubstrate.

FIG. 23 is a block diagram illustrating an active matrix type displaydevice (or apparatus) incorporating electro-optical elements, such asorganic electroluminescent elements as a preferred example of theelectro-optical devices, and an addressing scheme which may befabricated using the method or apparatus of the present invention. Inthe display device 200 shown in this figure, a plurality of scanninglines “gate”, a plurality of data lines “sig” extending in a directionthat intersects the direction in which the scanning lines “gate” extend,a plurality of common power supply lines “com” extending substantiallyparallel to the data lines “sig”, and a plurality of pixels 201 locatedat the intersections of the data lines “sig” and the scanning lines“gate” which are formed above a substrate.

Each pixel 201 comprises a first TFT 202, to which a scanning signal issupplied to the gate electrode through the scanning gate, a holdingcapacitor “cap” which holds an image signal supplied from the data line“sig” via the first TFT 202, a second TFT 203 in which the image signalheld by the holding capacitor “cap” is supplied to the gate electrode (asecond gate electrode), and an electro-optical element 204 such as anelectroluminescent element (indicated as a resistance) into which thedriving current flows from the common power supply line “com” when theelement 204 is electrically connected to the common power supply line“com” through the second TFT 203. The scanning lines “gate” areconnected to a first driver circuit 205 and the data lines “sig” areconnected to a second driver circuit 206. At least one of the firstdriver circuit 205 and the second driver circuit 206 can be preferablyformed above the substrate above which the first TFTs 202 and the secondTFTs 203 are formed. The TFT array(s) manufactured by the methodsaccording to the present invention can be preferably applied to at leastone of an array of the first TFTs 202 and the second TFTs 203, the firstdriver circuit 205, and the second driver circuit 206.

The present invention may therefore be used to fabricate displays andother devices which are to be incorporated in many types of equipmentsuch as mobile displays e.g. mobile phones, laptop personal computers,DVD players, cameras, field equipment; portable displays such as desktopcomputers, CCTV or photo albums; instrument panels such as vehicle oraircraft instrument panels; or industrial displays such as control roomequipment displays. In other words, an electro-optical device or displayto which the TFT array(s) manufactured by the methods according to thepresent invention is (are) applied as noted above can be incorporated inthe -many types of equipment, as exemplified above.

Various electronic apparatuses using electro-optical display devicesfabricated in accordance with the present invention will now bedescribed.

<1: Mobile Computer>

An example in which the display device fabricated in accordance with oneof the above embodiments is applied to a mobile personal computer willnow be described.

FIG. 24 is an isometric view illustrating the configuration of thispersonal computer. In the drawing, the personal computer 1100 isprovided with a body 1104 including a keyboard 1102 and a display unit1106. The display unit 1106 is implemented using a display panel 100fabricated according to the patterning method of the present invention,as described above.

<2: Portable Phone>

Next, an example in which the display device is applied to a displaysection of a portable phone will be described. FIG. 25 is an isometricview illustrating the configuration of the portable phone. In thedrawing, the portable phone 1200 is provided with a plurality ofoperation keys 1202, an earpiece 1204, a mouthpiece 1206, and a displaypanel 100. This display panel 100 is implemented using a display devicefabricated in accordance with the method of the present invention, asdescribed above.

<3: Digital Still Camera>

Next, a digital still camera using an OEL display device as a finderwill be described. FIG. 26 is an isometric view illustrating theconfiguration of the digital still camera and the connection to externaldevices in brief.

Typical cameras use sensitized films having light sensitive coatings andrecord optical images of objects by causing a chemical change in thelight sensitive coatings, whereas the digital still camera 1300generates imaging signals from the optical image of an object byphotoelectric conversion using, for example, a charge coupled device(CCD). The digital still camera 1300 is provided with an OEL element atthe back face of a case 1302 to perform display based on the imagingsignals from the CCD. Thus, the display panel 100 functions as a finderfor displaying the object. A photo acceptance unit 1304 includingoptical lenses and the CCD is provided at the front side (behind in thedrawing) of the case 1302.

When a cameraman determines the object image displayed in the OELelement panel 100 and releases the shutter, the image signals from theCCD are transmitted and stored to memories in a circuit board 1308. Inthe digital still camera 1300, video signal output terminals 1312 andinput/output terminals 1314 for data communication are provided on aside of the case 1302. As shown in the drawing, a television monitor1430 and a personal computer 1440 are connected to the video signalterminals 1312 and the input/output terminals 1314, respectively, ifnecessary. The imaging signals stored in the memories of the circuitboard 1308 are output to the television monitor 1430 and the personalcomputer 1440, by a given operation.

Examples of electronic apparatuses, other than the personal computershown in FIG. 24, the portable phone shown in FIG. 25, and the digitalstill camera shown in FIG. 26, include OEL element television sets,view-finder-type and monitoring-type video tape recorders, vehiclenavigation and instrumentation systems, pagers, electronic notebooks,portable calculators, word processors, workstations, TV telephones,point-of-sales system (POS) terminals, and devices provided with touchpanels. Of course, OEL devices fabricated using the method of thepresent invention can be applied not only to display sections of theseelectronic apparatuses but also to any other form of apparatus whichincorporates a display section. Furthermore, the display devicesfabricated in accordance with the present invention are also suitablefor a screen-type large area television which is very thin, flexible andlight in weight. It is possible therefore to paste or hang such largearea television on a wall. The flexible television can, if required, beconveniently rolled up when it is not used.

Printed circuit boards may also be fabricated using the technique of thepresent invention. Conventional printed circuit boards are fabricated byphotolithographic and etching techniques, which increase themanufacturing cost, even though they are a more cost-oriented devicethan other microelectronics devices, such as IC chips or passivedevices. High-resolution patterning is also required to achievehigh-density packaging. High-resolution interconnections on a board canbe easily and reliably be achieved using the present invention.

Colour filters for colour display applications may also be providedusing the present invention. Droplets of liquid containing dye orpigment are deposited accurately onto selected regions of a substrate. Amatrix format is frequently used with the droplets in extremely closeproximity to each other. In situ viewing can therefore prove to beextremely advantageous. After drying, the dye or pigments in thedroplets act as filter layers.

DNA sensor array chips may also be provided using the present invention.Solutions containing different DNAs are deposited onto an array ofreceiving sites separated by small gaps as provided by the chips.

Modifications to the above embodiments can be made whilst remainingwithin the scope of the invention. For example, the alignment marks havebeen described as being on the upper or first surface of the substrateonto which the polymer material is deposited. However, the alignmentmarks may also be provided on the lower or undersurface of thesubstrate.

Furthermore, the alignment marks have been shown located external to thearea 36 in which the polymer material is to be deposited to provide theactive pixels of the display device. However, the alignment marks mayalso be provided at selected locations within the area in which theactive pixels are to be formed, such as a linear array of alignmentmarks spaced along one edge, but within, the area 36. The alignmentmarks may be fabricated on the substrate during the process forproviding the bank structure.

Additionally, whilst the invention is described with respect to viewingthe alignment marks from an underside of the substrate, the alignmentmarks may also be viewed from the upper side of the substrate.

The deposition of material from the inkjet head may be carried out witha head having a single nozzle or an array of nozzles.

Furthermore, when a matrix array of alignment marks are provided and thesubstrate is provided with a bank structure, the pitch spacing of thealignment dots of the alignment array may be arranged to be n times thepitch spacing between wells of the bank structure, where n is aninteger. When an inkjet head having an array of nozzles is used, thepitch spacing of the matrix of alignment marks can be made tocorresponding to the pitch spacing of the nozzles so that the depositionperformance of a number or all of the nozzles can be checkedsimultaneously.

1. A method of patterning, the method comprising: providing an alignmentmark on a substrate and arranging the alignment mark to have opticalcontrast but no wettability contrast relative to the substrate;depositing a droplet including a material dissolved or dispersed in asolvent on a first area of a first surface of the substrate; and viewingthe droplet deposited on the first surface for checking a deviationbetween a position of the droplet deposited on the first surface and aposition of the alignment mark.
 2. A method as claimed in claim 1, theviewing of the droplet deposited on the first surface being carried outby observing the droplet deposited on the first surface from a secondsurface of the substrate opposite to the first surface.
 3. A method asclaimed in claim 1, the viewing of the droplet deposited on the firstsurface being carried out prior to removing the solvent from the dropletdeposited on the first surface.
 4. A method as claimed in claim 3wherein the droplet including the material is detected as it deposits onthe first surface of the substrate.
 5. A method as claimed in claim 1,wherein the droplet is provided on a further area of the substrateexternal to the first area.
 6. A method as claimed in claim 1, wherein afurther alignment mark is provided within the first area of thesubstrate.
 7. A method as claimed in claim 1, wherein the alignment markis provided as a cross shape.
 8. A method as claimed in claim 7, whereinthe cross shape alignment mark is selected to comprise a plurality ofradially extending leg portions symmetrically disposed in acircumferential direction.
 9. A method as claimed in claim 7, whereinthe cross shape alignment mark is selected to comprise three or four legportions.
 10. A method as claimed claim 1, wherein the alignment mark isselected to comprise a linear array of alignment marks spaced along atleast one edge of the substrate.
 11. A method as claimed in claim 1,wherein the alignment mark is selected to comprise a matrix array ofalignment marks.
 12. A method as claimed in claim 1, wherein thealignment mark is selected to comprise one or more linear arrays ofalignment marks spaced along at least one edge of the substrate and oneor more matrix arrays of alignment marks.
 13. A method as claimed inclaim 12, wherein the matrix array is selected such that a pitch spacingbetween alignment marks of the matrix array is n times the pitch spacingbetween wells of the patterned structure, where n is an integer.
 14. Amethod as claimed in claim 1, comprising: providing a patternedstructure including an array of wells for receiving the material in thefirst area of the substrate.
 15. A method as claimed in claim 14,wherein the droplet is deposited using an inkjet print head and theinkjet head is selected to comprise a multi-nozzle inkjet head and apitch spacing between the nozzles is selected to correspond to a pitchspacing between the wells of the patterned structure.
 16. A method asclaimed in claim 1, wherein an alignment dot of the material is providedperiodically by an ink jet print head during the deposition of thematerial onto the first area of the substrate.
 17. A method as claimedin claim 1, wherein the substrate is selected to comprise a rigidsubstrate of glass, silicon or plastics material.
 18. A method asclaimed in claim 1, wherein the substrate is selected to comprise aflexible plastics material.
 19. A method as claimed in claim 1,comprising: selecting the material to comprise a conjugated polymer. 20.A method as claimed in claim 19, comprising: irradiating the surface ofthe substrate with light of a wavelength to which the substrate issubstantially transparent when viewing an alignment dot of the material.21. A method as claimed in claim 20, wherein the light is selected tohave a wavelength which is greater than the wavelength of the absorptionedge of the conjugated polymer.
 22. A method as claimed in claim 1,comprising: using an image recognition technique to detect the dropletrelative to the alignment mark.
 23. A method of making a display deviceincluding the fabrication of light emitting elements using the method ofclaim
 1. 24. A method of patterning, the method comprising: providing analignment mark on a substrate; depositing a droplet including a materialdissolved or dispersed in a solvent on a first area of a first surfaceof the substrate; and viewing the droplet deposited on the first surfacefor checking a deviation between a position of the droplet deposited onthe first surface and a position of the alignment mark, wherein thealignment mark is selected to comprise one or more linear arrays ofalignment marks spaced along at least one edge of the substrate and oneor more matrix arrays of alignment marks, and further wherein the one ofthe matrix arrays is selected such that a pitch spacing betweenalignment marks of the one of the matrix arrays is n times the pitchspacing between wells of the patterned structure, where n is an integer.